Method of controlled catalytic heating of a subsurface formation



Dec. 14, 1965 E. B. HUNT ETAL 3,223,166

METHOD OF CONTROLLED CATALYTIC HEATING OF A SUBSURFACE FORMATION 2 Sheets-Sheet 1 Filed May 27, 1963 42 ELTON B. HUNT 45 HOWARD GREKEL INVENTORS.

FIG. -4 8 Z7 ATTORNEY.

Dec. 14, 1965 E. B. HUNT ETAL 3,223,166

METHOD OF CONTROLLED CATALYTIC HEATING OF A SUBSURFACE FORMATION Filed May 27, 1963 2 Sheets-Sheet 2 ELTON B. HUNT HOWARD GREKEL INVENTORS.

ATTORNEY.

United States Patent Ofitice 3,223,166 Patented Dec. 14, 1965 a corporation of Delaware Filed May 27, 1963, Ser. No. 283,155 4 Claims. (Cl. 166--38) The present invention relates to a method and apparatus for heating and stimulating oil wells. More particularly, it is concerned with a method and apparatus suitable for heating oil-bearing or similar formations to a temperature sufficient either for stimulating the flow of oil therefrom or for igniting such formation to recover oil by means of combustion.

Briefly, our invention contemplates supplying heat to an oil-bearing zone through the use of a catalytic heater wherein the temperature of the effluent from said heater is controlled by dilution with a bypassed, unoxidized portion of the feed to said heater. In this apparatus, heat is generated by the catalytic oxidation of a suitable mixture, typically a non-explosive mixture of methanol and air.

Many methods have been employed in the prior art for heating oil wells, e.g., by electrical means, by injecting heat transfer agents into the well such as steam, hot oil, etc., and by burning natural gas in the well bore. Considerable difiiculty has been encountered in the application of electric well heating owing to the highly corrosive nature of oil field brine, sulfur compounds, and other components of the fluids produced through the well bore. These fluids penetrate the innermost parts of the well heater, and even traces of moisture cause short-circuiting of the apparatus necessitating shutdown, removal and repair. These difficulties materially reduce the operating efficiency of such heating processes. Well bore liquids also penetrate and permeate the customary insulating materials, rendering them practically useless. These problems are peculiar to the well heating art and are not generally encountered in other applications of electrical heating.

One of the principal drawbacks of the gas or liquid fueled heaters is that it is extremely difficult to avoid damage to the casing and any well equipment present in the area where heat is being applied. This is due to the fact that the temperature at which heaters of this kind operate cannot be maintained at levels which such equipment can withstand. One of the difficulties with electrical heaters is their tendency to short out owing to hot spots developing through poor heat exchange, generally resulting from coke formation on the surface. With increasing thickness of the coke layer on the exterior of the heater, the temperature tends to build up until it exceeds the melting point of the heating elements causing the latter to fail.

Accordingly, it is an object of our invention to provide means for heating an underground formation whereby the maximum temperature generated can be readily and accurately controlled. It is another object of our invention to provide this temperature control by regulating the amount of the feed, contacted by the catalyst. It is a further object of our invention to regulate the quantity of feed coming in contact with the catalyst in the heater by the use of a temperature-responsive means. It is still another object of our invention to provide a bottom hole heater, the operation of which is based on the use of radiant heat transfer rather than convective heat transfer.

In the accompanying drawings, a number of embodiments of our invention are illustrated:

FIGURE 1 illustrates a heater design in which a portion of the feed is continuously bypassed around the catalyst bed and used to cool hot oxidation products coming from the efiluent end of said bed.

FIGURE 2 is a sectional plan view of FIGURE 1 taken along line 22.

FIGURE 3 is an elevational view, partly in section, showing another embodiment of our invention wherein the flow of feed through the catalyst bed is regulated, as to amount, by means of a temperature-responsive valve.

FIGURE 4 is a fragmentary sectional view of FIG- URE 3, showing how said valve functions to direct the bulk of the feed flow through the catalyst at lower temperatures.

FIGURES 5 and 6 are elevational views, partly in section, showing still another design of temperature-responsive valve means for direct flow of feed through the system.

FIGURE 7 is a plan sectional view, taken along line 7--7, of FIGURE 5 showing further details of the valve structure employed.

Referring now to FIGURE 1, the heater 4 is held to tube 6 by means of threaded coupling 8. Heater 4 includes an elongated housing or pipe 10, having concentrically arranged therein a tubing 12, held in position by means of spaced supports 14, welded or otherwise aflixed to tubing 12 and pipe 10. A suitable oxidation catalyst 16 is packed around tubing 12 and is held in place within the unit by means of hardware cloth 18, or equivalent material. While the length of catalyst bed 16 may vary widely, for the majority of applications this bed may be from 8 to 12 feet in length and have an actual diameter corresponding to 1 to 2 inches.

In FIGURE 3, a heater 20 is aflixed to ordinary well tubing 22 by means of threaded coupling 24. The heater consists primarily of an elongated housing or case 26 which, for example, may be from 2 to 3 inches in diameter. Inside case 26 is a concentrically spaced, cylindrically shaped container or vessel 28 made, for example, out of perforated steel. Alternatively, it may be constructed of a closed-end perforated sub. Vessel 28, having perforations 29, is held in place by means of tubing 30 attached to said vessel by threaded coupling 32 which, in turn, is connected to pipe 34 having perforations 36. Surrounding pipe 34 is a catalyst bed 38 held in position by upper wire screen 40 and a lower metal plate 42, having located in the center thereof an aperture 43 through which pipe 34 can pass during temperature fluctuations while the apparatus is in use. At the base of pipe 34, and resting on the bottom of vessel 28, is a conically or other suitably shaped plug 44, adapted to fit relatively snugly up into the lower interior portion of pipe 34. The base of vessel 28 contains perforations 45 through which gas passes when pipe 34 is in an unplugged position. FIGURE 3 illustrates the relationship of plug 44 to pipe 34 when some of the feed is bypassing catalyst bed 38, while FIGURE 4 shows the position of plug 44 with respect to pipe 34 when the major portion of the feed is being forced into catalyst bed 38-such condition existing at relatively low operating temperatures. Fins 46 may be added to the upper exterior of vessel 28 to increase the heat transfer characteristics of that portion of the heater, if desired. Also, in the space 48 insulation may be packed, if necessary, in order to prevent excessive preheating of the feed before it contacts the catalyst.

The materials out of which vessel 28 and tube 34 are constructed may vary. In general, it is'preferable to fabricate vessel 28 out of a metal having a relatively high coefficient of expansion with respect to the metal in tube 34. In this way, a more sensitive control of the heater operation can be maintained.

FIGURE 5 represents another design of heater employing a temperature-responsive valve means to controlthe amount of feed contacting the catalyst. In this design an elongated case 50- is afiixed to tube 52 by means of threaded coupling 54. Arranged concentrically within case 50 is a metal vessel 56, held in position by attachment to tubing 58. At the base of vessel 56 is a wire screen or metal grid 60 which serves to retain catalyst 62 in the vessel. Upward movement of catalyst 62 in vessel 56 is prevented by wire screen 64. In vessel 56, for example, about midway, is a ring of ports 66 which are shown to be in register with metal band 68 surrounding said vessel. This band is held in position by means of spaced supports 70, welded or otherwise aflfixed to case 50.

FIGURE 6 is identical to FIGURE 5, except ports 66 and band 68 are out of register, indicating the system is at a temperature above that desired and is being cooled through bypassing the feed via ports 66 and on up tubing 58.

In the catalytic heater design shown in FIGURE 1, the entire feed stream flows down tubing 6 and pipe 10. However, when it comes to tube 12, the stream divides with part passing through catalyst bed 16 and. the remainder flowing down through tube 12. The ratio of the flow through bed 16 is adjusted to the flow bypassed through tube 12 so that when these two streams mix after they emerge from heater 4, the resulting mixture downstream of the heater is at a temperature suitable for transferring heat to the oil outside.

Typically, operable temperatures lie within a range of from about 400 to about 1500 F. In regard to the matter of temperature, a level should be chosen such that excessive coking of the carbonaceous materials With which the surface of the heater comes in contact does not occur to an appreciable extent. Ordinarily, the higher temperatures, i.e., 1000 to about 1500 F., should be employed where it is desired to ignite the formation preparatory to undertaking an underground combustion operation. Where the heaters of our invention are used primarily for the purpose of reducing the viscosity of heavy oils, and/or to prevent excessive paraflin deposition in the well, heater skin temperatures of the order of from about 300 to about 500 F. are generally preferred.

In the heater design shown in FIGURE 1, the excess fuel in the bypass stream coming from tube 12 does not react appreciably in the absence of catalyst. Care is exercised to employ fuel-air mixtures that are outside the explosive limits; accordingly, the system is not dangerous. The final temperature obtained in the mixture of the two eflluent streams from heater 4 depends on a number of factors, such as feed flow rates and feed composition. For application of the heater shown in FIGURE 1, at higher temperatures tube 12 should be of smaller diameter or should be packed with an inert permeable material in an amount suflicient to increase the pressure drop across said tube so that an increased amount of feed tends to be diverted into the catalyst bed. Conversely, if lower temperatures are desired, the pressure drop across tube 12 should be decreased, for example, by increasing the diameter of tube 12, or by other obvious means.

In FIGURE 3, feed is conducted down connecting tube strings 30 and 34. The embodiment shown is operating at the high end of the temperature scale desired, since the bulk of the feed is flowing through aperture 43. The temperature of the system is controlled by circulating excess feed'out the bottom of pipe 34 through perforations 45, thereby cooling the gases coming out of catalyst bed 38. Vessel 28, which preferably has a substantially higher thermal coefficient of expansion than tubing 34, on heating tends to expand longitudinally. It will be appreciated, however, that it is possible to use the same kind of metal for vessel 28 and tubing 34 at the temperature differentials contemplated. In the case of a methanol-air feed, the temperature within tube 34 may be 400 F while the temperature of the catalyst bed 38 and vessel 28 can be 800 F., or higher.- This temperature differential is more than adequate to assure a substantial flow of cooler bypassed feed out the bottom of tube 34 and up and around the sides of vessel 28, bringing about a substantial lowering in temperature of the oxidation products flowing from the catalyst bed via perforations 29. This arrangement of plug 44 and the lower end of tube 34, as they move relative to one another, acts as a thermostat to control the cooling of gases coming from the catalyst bed so that they will not cause excessive coking of the oil with which the heater may be in contact.

Initially, the relationship of plug 44 to tube 34 is essentially as shown in FIGURE 4. There the bulk of the feed gas is prevented from bypassing the catalyst and is forced into bed 38 producing hot oxidation products that are vented on up the annulus between vessel 28 and case 26, eventually flowing out of the system via tubing 22.

In the type of heater described herein, heat transferred by radiation increases roughly as the fourth power of temperature. In the case of a heater involving heat transfer by convection, such heat transfer increases more or less linearly with temperature. Thus, the higher the catalyst temperature, the greater the proportion of heat transferred by radiation. With this type of heater, only about 10 square feet of radiating surface is necessary to radiate 1 million B.t.u. per day from a catalyst surface at 1000 F. to a pipe wall at a temperature of 500 F.

With the heater shown in FIGURES 5 and 6, feed gas flowing down the annulus between case 56 and case 50 is preheated by hot vent gas flowing upwardly through case 56. This also is the area where most of the heat is transferred to the oil in the well. 'Part of this heat is transferred by convection from the feed gas as it is being preheated, and part by radiation. The preheated feed flows up through catalyst bed 62, as shown in FIGURE 5, where oxidation occurs and heat is generated. The portion of case 50 directly opposite catalyst bed 62 may have to be insulated to prevent too much cooling of the preheated feed prior to its entry into the catalyst bed. In this connection, preheat temperatures of from 200 to about 600 F. should generally be employed. Methanol-air mixtures, for example, need not be preheated as high as mixtures of propane and air in order for the desired reaction to occur on contact with the catalyst. Ordinarily, propaneair mixtures with the platinum catalyst we have employed should be preheated to a temperature of about 600 F. compared to about 200 F. for a mixture of methanol and air. In this regard, attention should be called to the fact that while a feed mixture of methanol and air is relatively cheap, light hydrocarbon-air mixtures, such as natural gas and air, or propane and air, are much less expensive. Accordingly, it may be found desirable, in some instances, once sufliciently high operating temperatures are reached with methanol-air feed mixtures, to switch to a natural gasor propane-air mixture for further operation.

The hot vent gas leaves catalyst bed 62 and flows up through tubing 58 where it loses part of its heat to preheat the feed and part to pipe 52, and thus transfers heat to the oil in the well. The design is such that'the vent gas leaving the heater is below coking temperature of the crude oil.

It is possible to contemplate conditions such that the steady state heat transfer rate to the reservoir from the heater is not exceeded by the heat generation rate of the heater. If, however, the heat thus generated does exceed the heat transferred to the reservoir, the temperature-responsive valve comprising essentially ports 66 and metal band 68 serves to maintain the system in proper heat balance. This valve is opened by the longitudinal expansion of vessel 56 which may be at a temperature of, for example, 800 to 900 F., whereas the walls of case 50 are only about 400 F. When ports 66 are opened by their downward movement relative to metal band 58, some of the feed bypasses catalyst 62, flows into vessel 56 via ports 66, and travels out of the system via pipe 52.. In this way the rate of heat generation is automatically reduced whenever the apparatus tends to overheat.

The fuel portion of the feed which is to be contacted with the catalyst in accordance with our invention may be selected from a wide variety of substances such as, for example, light hydrocarbons, typically natural gas, propane, butane and unsaturated derivatives thereof, kerosene, crude oil, oxygenated organic chemicals, such as the lower molecular weight alcohols, for example, methanol, and the like. Mixtures, of course, of two or more of the foregoing materials may be usedin gaseous or liquid form as the fuel component of the feed. In general, We prefer to employ air or oxygen-rich fuel mixtures; however, our invention also contemplates the use of fuel-rich mixtures.

Generally speaking, space velocities as high as 100,000 s.c.f.h. per cubic foot of catalyst may be employed. Substantially complete oxidation of the fuel can generally be accomplished at space velocities of this order when fuel-air mixture preheat temperatures, within the range disclosed above, are used.

The temperature at which the heater operates depends on a number of factors such as, for example, the composition of the feed and the rate of heat generation and heat loss. As the fuel content increases, under an otherwise fixed set of conditions, the generated temperature will be observed to increase. For example, in the case of methanol-air mixtures, the adiabatic temperature rise in the bed is found to increase linearly over a methanol concentration of 1 to 5 mol percent and a temperature range of from 400 to 1500 F.

The catalysts used may be selected from a wide list of materials and form no part of our invention. Typically, catalysts suitable for oxidation of the feeds contemplated herein include metals of platinum groups and their oxides, etc. These catalysts are preferably used in very dilute concentrations, e.g., 0.05 to about 0.5 weight percent, and may be supported on materials having a large surface area, such as pumice, aluminum oxide, metal wool, for example, stainless steel wool, and the like. Supported platinum actalyst suitable for this purpose is manufactured by the Chemetron Corporation of Louisville, Ky., and is identified as catalyst (3-43. In operation, the portion of catalyst apparently entering into the oxidation reaction is that with which the feed mixture first comes in contact.

It will be apparent that operation of the thermostatically controlled heaters shown herein will depend on the thermal characteristics of the metal, or metals, from which they are constructed and the existing temperature difi'erential. For example, with an all stainless steel heater 12 feet long, the housing or outer shell will expand about onefourth of an inch where the temperature difference between the hotter and cooler elements of the heater is about 300 F. Greater expansion, of course, can be obtained at the same temperature differential by use of metals having different thermal coefficients of expansion.

It is to be understood that while our invention is particularly applicable to the recovery of hydrocarbons from liquid petroleum reservoirs, it is equally suited to the recovery of valuable products from other subsurface combustible materials such as, for example, oil shale, tar sand, coal and the like.

We claim:

1. A method for heating a subsurface formation containing a combustible material, said formation being penetrated by a well wherein a body of an oxidation catalyst is placed in said well and at the appropriate level of said formation, and conducting a nonexplosive, fuel-oxygen containing gas mixture through said catalyst to produce hot products of combustion which pass in heat exchange relation with said formation, the improvement which comprises controlling the temperature of said products by bypassing a regulated portion of said fuel-oxygen containing gas mixture around said catalyst, the volume of said mixture bypassed around said catalyst varying directly with the temperature of said products, and thereafter combining said portion with said products.

2. The method of claim 1 in which the portion of said bypassed mixture is sufficient when combined with said products to produce a final gaseous mixture having a temperature of from about 500 to about 1100 F.

3. The method of claim 1 in which the fuel employed is natural gas and the oxygen-containing gas is air.

4. The method of claim 1 in which the fuel employed is methanol and the oxygen-containing gas is air.

References Cited by the Examiner UNITED STATES PATENTS 2,877,847 3/1959 Pelzer et al l6639 2,985,240 5/1961 Emery 166-59 3,072,191 1/1963 Bond et al 16639 3,107,728 10/1963 Kehn 16659 3,127,935 4/1964 Poettmann et a1 16611 OTHER REFERENCES Hackhs Chemical Dictoionary, 3rd edition (1944), The B-lakiston Company, Philadelphia, Pennsylvania, page 5 32 relied on.

CHARLES E. OCONNELL, Primary Examiner.

BENJAMIN HERSH, Examiner. 

1. A METHOD FOR HEATING A SUBSURFACE FORMATION CONTAINING A COMBUSTIBLE MATERIAL, SAID FORMATION BEING PENETRATED BY A WELL WHEREIN A BODY OF AN OXIDATION CATALYST IS PLACED IN SAID WELL AND AT THE APPROPRIATE LEVEL OF SAID FORMATION, AND CONDUCTING A NONEXPLOSIVE, FUEL-OXYGEN CONTAINING GAS MIXTURE THROUGH SAID CATALYST TO PRODUCE HOT PRODUCTS OF COMBUSTION WHICH PASS IN HEAT EXCHANGE RELATION WITH SAID FORMATION, THE IMPROVEMENT WHICH COMPRISES CONTROLLING THE TEMPERATURE OF SAID PRODUCTS BY BYPASSING A REGULATED PORTION OF SAID FUEL-OXYGEN CONTAINING GAS MIXTURE AROUND SAID CATALYST, THE VOLUME OF SAID MIXTURE BYPASSED AROUND SAID CATALYST VARYING DIRECTLY WITH THE TEMPERATURE OF SAID PRODUCTS, AND THEREAFTER COMBINING SAID PORTION WITH SAID PRODUCTS. 